Home automation systems for controlling devices with various functions such as lighting and audio equipment within a building has evolved towards a “smart-home” concept, where different input/output (I/O) devices with a wide range of functions are remotely controlled by a central controller. Such systems are constructed as networks with a plurality of nodes which can be controllers, I/O devices, or dedicated signal repeaters or amplifiers.
The quality of such systems are typically defined by a number of parameters:                Reliability. How often is a signal erroneous received by the intended receiver, or not received at all. The reliability can be quantified in a number of ways such as MTBF or bit error rate, and a many types of errors can be detected and corrected automatically by the system. Reliability, as a quality parameter, is best described as whether the user regularly experiences that the system does not perform the desired task.        Range/coverage. How large a network can be supported by the system, and is there any required minimum density of signal repeaters or amplifiers. Also, can a node be connected to the network to send and receive signals anywhere within the range of the network, or are there any “dead spots”.        Versatility. Which types of I/O devices and functions can be controlled by the system, and can the network support the required signals used for these applications. Can the network topology be expanded with new functionalities without undue burden and does the system/network support a large number of nodes. These considerations are often related to a communication protocol of the system, and depends on whether the communication protocol is constructed with a specific application in mind or optimized to a specific type of I/O devices.        Flexibility. The system should be easy to install, set up, change, and use. Thus, the learning of new nodes and configuring of routes for signal transmission should be automated to at least some degree. Also, the programming and use of functions, as well as expansion of the system, should be a simple and straightforward tasks for the user. This even more so in home automation systems for use in private homes.        
Automation systems based on wired networks provide a high quality in the first three quality parameters and very seldomly in the fourth parameter, and are often the primary choice in high capacity and high security systems where a high quality is required. However, wired networks have a number of obvious drawbacks:                Dependency of medium. The disconnection of an important wire section may freeze the entire network.        Low flexibility. Wired networks are very inflexible, if a node is desired at a position outside the existing network, or at a position within the network, which is connected with wire, a new wire branch must be drawn and connected to the network.        Installation. The initial installation of the network, drawing and connecting wire, as well as extension of an existing network are laborious and often require assistance from professional personnel.        Price. The costs in connection with installation and extension of wired networks are extremely high. If a wired network for an automation system is to be installed in a family-size private home, the expenses for having the wires drawn and connected may add up to U.S. Dollars 10.000 if installed during construction of the house, and to U.S. Dollars 25.000 if to be installed in an existing house. On top of this comes the price for controllers, I/O devices, and signal repeaters or amplifiers.        
Although wired networks generally provide a better quality, wireless networks have become more and more popular as a cheap and easy accessible network solution. Wireless networks clearly overcome the above-mentioned drawbacks of wired networks. However, most existing low cost wireless automation systems have a low quality in most of the mentioned parameters. Higher bandwidth wireless automation systems, are typically very complex and require higher processing power whereby the price get close to the price for a wired network.
U.S. Pat. No. 5,905,442 discloses a wireless automation system with a centralized remote control which controls I/O devices for providing electrical power to appliances from power outlets of the power mains in building. The remote control and I/O devices comprise RF transceivers, and the system includes dedicated repeater units for repeating signals to I/O devices out of the range of the remote control.
U.S. Pat. No. 5,875,179 describes a method for synchronising communications over a backbone architecture in a wireless network. The system invokes two controllers, one of which is a master and another which is an alternate master which will be activated only when the master is out of work. Dedicated repeaters and I/O devices in the system are commonly designated as nodes, however, it is clear from the context that there is distinct functional difference between repeater nodes and end (I/O) nodes.
U.S. Pat. No. 4,427,968 discloses a wireless automation system with flexible message routing. A central station produces a signal for a I/O device, the signal contains a route code, an address code, an identifying code and a message code. Dedicated repeaters in the architecture receive the signals and follow a specified procedure for repeating signal. Repeaters may also be addressed as end nodes, e.g. in order for the controller to download routing tables.
U.S. Pat. No. 4,250,489 describes a communication system having dedicated repeaters organised in a pyramidal configuration. The repeaters are bidirectionally addressable and may receive interrogation signals telling a repeater that it is the last repeater in the chain. The repeaters are not connected to appliances and do not perform any functions besides repeating and routing signals.